QPQ & Welding

[QCPEEWEE]

Hello everyone.
I have some questions on some QPQ items on an assembly I have built. Question is, Will any of the items be effected if I weld on the assembly it's self? As in we would have to pre-heat to 125°F. Now where the preheat will be applied isn't QPQ although parts that are QPQ are in close proximity. Second question. Has anyone ever heard of welding on QPQ parts. I would imagine the QPQ would be affected. If anyone could direct me in the right direction, it would be greatly appreciated. Thanks in advance.

QCPEEWEE

 

[metengr]

Could you please identify what QPQ means to the general public?

 

[boo1]

Quench polish quench (QPQ) is a specialized type of nitrocarburizing case hardening that increases corrosion resistance.

 

[boo1]

increases wear resistance to

http://www.houstonplating.com/our-services/qpq.html

http://www.burlingtoneng.com/wear_resistance.html

 

[QCPEEWEE]

My apologies for on not clarifying what QPQ is. b001 gave a brief description.

 

[CoryPad]

You cannot weld over the QPQ layer, it will result in extensive porosity and cracking.

Preheating a QPQ to 125 degrees F will not be detrimental.

 

[QCPEEWEE]

CoryPad thanks for the info. That's what I kind of figured would happen due to the nitriding layer. Now what if I were to grind it down to bare metal?

 

[tbuelna]

QCPEEWEE-

The processing temps used for QPQ liquid salt bath nitrocarburize (AMS 2753) are around 1075degF during the nitrocarburizing step (the first "Q") and around 750degF during the post oxidizing step (the second "Q"). Alloy steels that are treated with QPQ are usually tempered at a temperature just slightly above the max processing temp prior to nitrocarburizing.

Just out of curiosity was the 125degF weld preheat number in your OP a typo? That's not much of a preheat.

If you are welding in close proximity to the QPQ surface you will want to cover it during welding if possible. The surface is tumble polished between the thermal process steps (the "P" in QPQ) to remove heat treat scale and improve the final surface texture. The smooth finished surface is one desirable characteristic of QPQ, and it would easily be damaged by contact from weld spatter.

Regarding the question in your last post about removing the nitrocarburized surface in an area to be welded, you should be able to apply a copper plating mask to any surfaces that you don't want treated. Much easier than grinding away the case hardened surfaces.

 

[CoryPad]

Terry,

In the automotive industry, it would be easier to do grinding than copper plating.


QCPEEWEE,

If you grind to base metal, you could weld.

 

[QCPEEWEE]

tbuelna the preheat of 125 in the minimum required temp per AWS D1.1 for 1" thick A514.
CoryPad thanks for your info. Now another quick question what book(s) would be good to have to see about weldabilty of steels? I sometimes get to have to write up dissimilar steel WPS and also to see if I need to PWHT or not.

 

[CoryPad]

In addition to AWS standards, the ASM Handbook series is an excellent reference for learning about steel weldability (and any other metallurgical information).